The use of gaze trackers (also referred to as eye trackers) in human-computer interaction is becoming more feasible now that gaze tracking systems are becoming more portable and affordable. However, existing gaze trackers require calibration in order to work effectively. Typically, calibration requires a user to fixate on a sequence of points before a gaze tracker can be used. Over time, the system may need recalibrating, especially if the user moves around (leaves their desk), or if ambient conditions change, such as lighting levels. All of this is disruptive to a user's work or other activities, and makes the use of gaze tracking either cumbersome or distracting, or simply inaccurate.
Gaze trackers measure changes in gaze direction of a subject, such as a person operating a computing device. The point of gaze is the point where a subject is looking and the gaze direction is the direction of a line of sight from the eye to the point of gaze. Thus to compute gaze direction, information about head or eye location is used. This may be achieved by fixing the head location at a known place, using a bite bar, a forehead support or similar apparatus. Where the head is free to move, the head position and/or eye location is tracked, using image data or in other ways.
Many types of gaze tracker are known including those which measure movement of an object attached to the eye (such as a special contact lens), those which use optical methods for measuring eye motion, and those which measure electric potentials around the eyes. Where gaze direction is measured using any of these types of gaze tracker, calibration is an ongoing problem.
The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known gaze tracker calibration systems.